DE69834551T2 - COEXTRUDED TRACKED FILMS - Google Patents

Abstract

The invention is an oriented multilayer film comprising at least one outer layer comprising from 50 to 100 wt.% of said outer layer of an ethylene copolymer having a density of 0.900-0.935 g/cm<3> and a CDBI of 50-95 % said outer layer being in contact with a polypropylene core layer, and said film having been made by coextrusion of said ethylene copolymer and said polypropylene layer and subsequent orientation. The coextruded layers can be uniaxially oriented biaxially oriented on tenter equipment without difficulties caused by the presence of low molecular weight amorphous polymer fractions inherently present in traditional Ziegler-Natta linear low density polyethylene. The optical properties of biaxially oriented polypropylene films can be retained while the sealing temperature is lowered and the heat seal strength and the hot tack performance properties are improved.

Description

BACKGROUND OF THE INVENTION Field of the Invention

The The invention relates to an oriented multilayer film which is at least a layer of ethylene-based polymer. Especially the invention relates to a multilayer film produced, wherein at least one layer of ethylene-based random copolymer and the film was coextruded before being used for orientation was stretched.

description of the prior art

oriented Multilayer films are an important class of industrial products, especially when wrapping or packing different ones Products are commercially available. In particular, is oriented Foil with isotactic polypropylene because of its high barrier properties, Clarity and stiffness known to be useful. Polypropylene for oriented Films are typically isotactic homopolymer, or are modified Polypropylene blends of isotactic polypropylene with others isotactic polypropylene, e.g. through other melt flow rates (MFRs) or tacticity differs, atactic polypropylene, syndiotactic polypropylene, polypropylene random copolymers with small amounts of ethylene or higher α-olefins, and ethylene copolymers, see, e.g. US-A-4,950,720 and WO 96/02386. As in US-A-4 No. 921,749 and the related art, others may also be given Components such as petroleum resins be added to properties such as heat-sealing performance, gas permeability and to modify stiffness. Such oriented polypropylene, especially biaxially oriented polypropylene (BOPP), has many desired Properties. However, excellent heat sealing and heat sealing count not because of it, such films at operating temperatures, the for the efficient commercial practice are suitable for use in essential heat-sealing and hot tacking performance lacking.

The not pre-published WO 97/44178 discloses a coextruded blown film comprising an inside layer, a middle layer and an outside layer having. According to the examples 1 and 2, the middle layer is a polypropylene and the inner side and outside layers include an LLDPE while according to the examples 3 and 4, the middle layer is a polypropylene, the outside layer is a blend of LLDPE and LDPE and the inside layer is LLDPE.

The not pre-published EP-A-0 802 046 discloses a three-layer film having a first outer layer of polypropylene homopolymer or propylene copolymer, a second Inner layer, which includes LLDPE, and a third heat-sealable Layer, with the heat-sealable Layer a polyethylene homopolymer or copolymer or a mixture polyethylene homopolymer or copolymer and propylene homopolymer or copolymer.

The nichtvorveröffentlichte WO 98/37141 discloses a three-layer ABC film, wherein layer A LLDPE includes. Layer B may be selected from a large group including materials Propylene polymers. Layer C is random copolymer of propylene with up to 20% by weight of ethylene.

WO 92/14784 proposes heat-sealable blend compositions to be suitable for films and film structures containing from 30 to 70% by weight of low melting polymer, the ethylene based copolymer having a density of from 0.88 g / cm ³ to 0.915 g / cm ³ (a), a MWD of not more than 3.5 and a breadth index of the composition distribution of greater than 70% and (b) different from (a) and 70 to 30 wt% propylene-based polymer having 88 mol% to 100 mole% of propylene and 12 mole% to 0 mole% of propylene other than α-olefin.

The WO 95/13321 suggests heat-sealed Article and heat sealable Films containing a polymer mixture of first polymer with narrow molecular weight and composition distribution and second polymer having a broad molecular weight distribution and composition distribution.

Accordingly, various polymer layers have been used or proposed as heat-sealing layers for biaxially oriented polypropylene film. Among the commercially used and taught in the patent literature are ethylene-based and propylene-based polyolefins. Preferred heat seal layers for BOPP have typically been high-propylene polyolefins in the past, eg, propylene-ethylene copolymers having from 1 to 20 weight percent of ethylene and propylene-ethylene-butene terpolymers of up to 10 weight percent each of ethylene and butene and mixtures thereof with other olefin polymers, see for example US-A-4,643,954 (LLDPE with propylene terpolymer) and US-A-4,921,749 (propylene-ethylene copoly mere) and the other listed above. This polymer choice reduces the chemical diversity of the sealant layer and core layers, allowing good adhesion between them, but results in the need for subsequent heat sealing to be performed at temperatures at or above 120 ° C, which provides for long contact time with heating elements or high heat input required to reach the necessary temperature ranges.

Summary the invention

The invention consists of an oriented multilayer film which comprises (a) at least one outer layer comprising from 50 to 100% by weight of ethylene copolymer having a density of from 0.900 to 0.935 g / cm ³ and a composition distribution breadth index (CDBI). from 50 to 95%, (b) a polypropylene core layer, said at least one outer layer being in contact with said polypropylene core layer, and (c) a second outer layer, said second outer layer being in contact with said propylene core layer, said film passing through Coextrusion of the at least one outer layer, the core layer and the second outer layer and subsequent orientation except random copolymer of propylene and at most 20% by weight of ethylene or terpolymer of propylene, ethylene and butene as the second outer layer.

Preferably, the ethylene copolymer has outer or skin layer, or have the ethylene copolymer outer or skin layers, a molecular weight distribution (MWD, M _w / M _n ) of 1.8 to 3.5, and a melt index (MI) of 0, 5 to 10 g / 10 min (ASTM D 1238, 190 ° C, 2.16 kg). The co-extruded layers can be biaxially oriented on tenter equipment produced by the presence of low molecular weight amorphous polymer fractions inherently present in traditional low density linear Ziegler-Natta polyethylene. Problems with unwanted adhesion to drums and baking during processing and the presence of extractables are substantially eliminated in the films thus produced. The optical properties of biaxially oriented polypropylene films (BOPP) are maintained, lowering the sealing temperature and improving the heat seal strength and heat sealing properties. The ethylene copolymer heat seal layer thus provides a practical, economical solution for the production of heat seal BOPPs for rigid, flexible as well as heat shrinkable packaging.

Short description the figures

1 Figure 3 is a graph of the heat seal (1a) and hot tack (1b) performance of the film of the Examples. The figures are the hot tack and seal behavior of 10% mLLDPE and 90% polypropylene of biaxially oriented coextruded films.

detailed Description of the invention

Copolymers useful in the present invention are commercially available and can be prepared with catalysts having substantially singular active sites, such as metallocene catalysts. The use of the term "substantially singular active site catalyst" refers to any polymerization catalyst which provides a narrow molecular weight distribution (MWD, M _w / M _n ) and narrow composition distribution as determined by the composition distribution breadth index (CDBI). Commercially available products include more specifically, the metallocene LLDPE resins (m-LLDPE), which Exxon Chemical Co., Houston, Texas, USA, as EXCEED ^® 350D60 (ethylene-hexene copolymer, MI = 1.0, density 0.917 g / cm ³⁾ and 377L60 (ethylene-hexene copolymer, MI = 1.0, density 0.922) are marketed, and the metallocene plastomer ethylene copolymers, sold under the trade name EXACT ^®, available from Exxon Chemical Co ., and AFFINITY ^®, available from marketed Dow Chemical Company, Midland, Michigan, USA, where have such plastomers densities or below about 0,900. Typically, the ethylene copolymers comprise as comonomers any C ₃ to C ₁₂ α-olefin, preferably one or more C ₄ to C ₈ α-olefin (s). Comonomer content is determined by the density measured, preferably in the range of 0.910 to 0.925 g / cm ³ , most preferably 0.915 to 0.925 g / cm ³ . Preferably, the molecular weight of the ethylene copolymers of this invention, measured as MI (polyethylene melt index, ASTM D 1238), is in the range of about 0.7 to 8.0, and most preferably 0.7 to 5.0. The MWD is typically 2.0 to 3.5, preferably 2.0 to 2.7. The CDBI is preferably above 55%, most preferably above 65% by weight. The melt index ratios (MIR, I ₂₁ / I ₂ ) of the suitable ethylene copolymers are typically in the range of 16 to 50.

Additional ethylene copolymer compositions which ge according to the invention as sealing layers include polyethylene blend compositions wherein the above-defined ethylene copolymer is at least 50 weight percent and moreover, there are minor amounts of substantially compatible ethylene-based homopolymers or copolymers containing ethylene and one or more C ₃ to C ₁₂ . α-olefins, cyclic olefins, vinylaromatic and polar vinyl monomers such as norbornene, alkyl-substituted norbornenes, styrene, alkyl-substituted styrenes, vinyl acetate, acrylic acid, methyl acrylate, butyl acrylate, etc. The blend compositions comprising ethylene-α-olefin copolymers are preferred those having a total density of 0.910 to 0.925 and a MI of 0.7 to 5.0 g / 10 min. For blends comprising the other ethylene copolymers, the copolymers are preferably those with from 2 to 5 mole percent comonomer and equivalent MI. Specific blend polyethylenes include any of LDPE, plastomers, LLDPE, MLDPE or HDPE, which terms are used as in the prior art, prepared by Ziegler-Natta polymerization, substantially single-site coordination polymerization, and high-pressure free-radical polymerization. Vinylmonomers comprising polymers include ethylene / vinyl acetate (EVA), ethylene / vinyl alcohol (EVOH), ethylene / acrylic acid (EAA), and ethylene / methyl acrylate (EMA). Ethylene copolymers suitable for blends are those having an ethylene content sufficient to provide such ethylene crystallinity that ensures that the blend compositions do not undergo strong phase separation upon cooling within the blend compositions upon cooling.

Low crystallinity copolymers, and thus a density of or below 0.915 ("VLDPE"), including certain plastomer-ethylene copolymers having C ₄ to C ₈ alpha-olefins with densities of from 0.870 to 0.915 g / cm ³ are known as Blend components are particularly preferred when present in sufficient amounts to permit higher road speeds because of the presence of lower melting point, lower density copolymers. The VLDPE copolymers are preferably present in an amount of up to 30% by weight, preferably 15 to 20% by weight. Further description of the VLDPEs and their uses in film applications can be found in US-A-5,206,075 and US-A-5,359,792.

A suitable polypropylene core or outer layer, or suitable polypropylene core or outer layers, includes or comprises any of the isotactic polypropylene compositions or blends which are suitably known for use as uniaxially or biaxially oriented films. Both traditional Ziegler-Natta polypropylene resins and those of the more recent, essentially singularly active, catalysts are suitable if they have sufficient molecular weights to ensure tailoring the melt viscosity suitable for coextrusion. Such propylene polymers having a melt flow rate "MFR" (ASTM D 1238, 230 ° C, 2.16 kg) of from about 1.0 to about 40 are suitable, preferably to 10, most preferably 6.0. The polypropylene products with film quality ESCORENE ^® PP4592 E7, PP4372 and PP4252 E1 from Exxon Chemical Co. are particularly suitable. Additionally, random polypropylene copolymers having up to about 15 mole percent of at least one C ₂ to C ₈ α-olefin other than propylene are useful as a co-extrudable polypropylene layer, as a core, outer, or interlayer.

method for the production of coextruded films are good in the art known. For the present invention will be the ethylene copolymer compositions, which are suitable as sealing layers, and the polypropylene compositions separately, but at the same time, extruded and aligned before orientation Co-extrusion connected. Because the melt viscosity of the preferred ethylene copolymers, or of these comprehensive mixtures, at processing temperatures, which are necessary to extrude the polypropylene film, high is enough to get a sufficient dimensional stability, can both thick and thin Foils of uniform thickness over the film surface to be obtained. The lack of low-amorphous fractions Molecular weight and sufficiently high melting points of the ethylene copolymer compositions allow excellent processing without sticking to the processing equipment while, however the most appropriate dimensional stability is maintained.

One preferred method for producing the films of the invention includes a co-extrusion process with subsequent orientation of the co-extrudate.

Even though already known in the industry was that polymers with lower Melting point can be applied by a coating process can, in which the polymer is in the molten or softened state extruding the preformed polymer film with a higher softening point It is also known that the use of chemical dissimilar Polymers to inadequate adhesion between the layers to lead can. That's why it becomes common the use of additional Recommended binding layers (or adhesive layers) that are capable are to adhere to both layers if two different polymers to be combined with each other, see e.g. J. Stepek et al., Polymers As Materials For Packaging, Chapter 5, pp. 346-349 (Ellis Horwood Ltd., 1987, English language edition).

The The present invention is based on the finding that the Use of multiple coextrusion extruders with two or more Stream, at least one of which is the ethylene copolymer compositions and another of these are the polypropylene compositions provides and simultaneous feeding in a multi-channel nozzle, so that the two layers are in contact with each other for slot die extrusion and subsequent orientation, for the production of films Can be used, which has excellent adhesion between maintain the layers and excellent composite film properties, without the need for additional Binding or adhesive layers. The excellent clarity of BOPP is maintained while the seal start temperature is lowered and the sealing properties the film can be improved, both in overall strength as well without enough heat supplied must be to soften the polypropylene layer. Because the seal layer polymers Softening points according to the invention from 80 to 100 ° C, and melting points of 100 to 120 ° C, own, is the effective heat sealing temperature lower than that of typical sealant layers with propylene copolymers, it can be reached faster during processing and leads use in manufacturing at higher road speeds.

Inventive films shut down in particular oriented two-layer A / B films with the sealing layer A and an outer layer B of polypropylene on, or three-layer A / B / A films with two sealant layers A on each side of the polypropylene core layer B. Additional layers or treatments the films in layer B are also suitable, such as metallization or corona discharge treatment, wherein the addition of other barrier layers or tie layers are also good in the art than in any Combination for special commercial article applicable is known.

The Heat seal layer A may be on one side of a multilayer film and may be considered another core layer can be used, or on both sides, to an additional Heat seal layer to build. Such composite films all enjoy the benefits of improved Adhesion of layers A and B and the compatibility of the film with combined Layers for orientation, in particular for uniaxial orientation and biannual orientation, such as in use Orientation method with tenter. In addition, the broad ones deliver Plateau sealing temperatures, i. 110 ° C to 140 ° C, a significant advantage for industrial Procedures in which accurate temperature control is uneconomical or somehow not available is. The by pressing and co-heating of two such Layers of formed heat seals usually fail by peeling in the specified plateau range, if they have a breaking strength of Be subjected to 1.32 to 6.6 kg (0.6 to 3.0 lbs). This failure mechanism provides excellent characteristics for peelable seals used in the Packaging industry are useful, especially for flexible Packagings. higher peel strengths (> 6.6 kg (3.0 lb)), e.g. 6.6 to 13.2 kg (3.0 to 6.0 lb) can be achieved by the thickness of the heat seal layer described here by way of example elevated and / or by adding one or more additional coextruded binding or adhesive layers, such as those containing ethylene or propylene copolymers.

The polymer characterizations depicted in this application were performed under the following conditions and procedures. The MI was determined as described in ASTM D 1238. M _w , M _n and M _w / M _n (MWD) were determined by gel permeation chromatography (GPC) using a differential refraction index (DRI) detector, ie a Waters 150C GPC instrument with DRI detectors. The CDBI was determined according to the method described in columns 7 and 8 of WO 93/03093. The density for both the polyethylene and polypropylene was determined according to ASTM D792.

Examples

• I. TM Long Experiments: Co-extruded structures were cast on a Killion Laboratory Road and then biaxially oriented (6x6) on a TM Long Road to produce a two-layer film A / B and a three-layer film ABA. which had one or two 0.2 mil (0.2 mil) final thickness heat sealing layers and a 10.16 μm (0.4 mil) polypropylene core layer. The ethylene copolymer heat seal layers were prepared from EXCEED ^® 350D60 (ethylene / hexene copolymer, MI = 1.0, density = 0.917 g / cm ³⁾ - or 377L60 (ethylene-hexene copolymer, MI = 1.0, density = 0.922 g / cm ³ ) resins were extruded and the polypropylene layer was extruded from PD4252E1, all available from Exxon Chemical Co.
• II. Pilot Plant Road Experiments: The films of Tables 1 through 4 below were prepared on a Black Clawson Road and biaxially oriented on a tenter as described in Tables 1 through 3 below. The film properties are shown in Table 4. Table 1
  

• * Streckspalt mit 0,081 cm (0,032''). Die Ziehgeschwindigkeit wurde so eingestellt, um das gewünschte MD-Ziehverhältnis zu erreichen.

Tabelle 3

Tabelle 4 Folieneigenschaften von biaxial orientierter co-extrudierter Folie

• * Planungsziehverhältnisse wurden bei dem Versuch bestimmt. Die tatsächlichen Ziehverhältnisse wurden aus den hergestellten Folien bestimmt.
• ** Reißwerte basieren auf der Verwendung eines 200 g-Pendels. Die ASTM sagt, dass Reißwerte durch Ablesen zwischen 20 und 60% des Pendelgewichts erhalten werden sollen. Die Reißwerte waren derart niedrig, dass dies unmöglich war.
• *** Unter Verwendung von 2 Einschussbögen aus HDPE.

Screw speed and specific output were the same for all slides. 8.89 cm (3.5 '') 30/1 L / D, 1.06 m (42 '') wide nozzle. Air knife pinning. The first chill roll was (87 ° F) 31 ° C and the second chill roll was (75 ° F) 24 ° C. The road speed was adjusted to reach the desired level. All other processing conditions were constant. Table 2

• * Elongation gap 0.081 cm (0.032 "). The pull rate was adjusted to achieve the desired MD draw ratio.

Table 3

Table 4 Film properties of biaxially oriented coextruded film

• * Planning drawing ratios were determined during the experiment. The actual draw ratios were determined from the films produced.
• ** Tear values are based on the use of a 200 g pendulum. The ASTM says that tear values should be obtained by reading between 20 and 60% of the pendulum weight. The tear values were so low that this was impossible.
• *** Using 2 slip sheets of HDPE.

• III. The films of the following examples 1 to 4 were made by co-extruding and casting a two-layer tape and then biaxially oriented. The casting took place on a Black Clawson Road and orientation on a pilot tenter. The resulting films are in Table 5 and those for orienting the films used the pilot tenter Conditions are summarized in Table 6.

Tabelle 6 b. MD-Orientierung

b. TD-Orientierung

The properties of the coextruded film were similar to those of biaxially oriented polypropylene film without the heat seal layer. For example, the products retained excellent optical properties (haze and gloss) and the Elmendorf tear strength was substantially the same, 0.0039 g / μm (0.10 g / mil). The ethylene copolymer heat seal layer was only 0.7 to 3.0 μm (0.03 to 0.12 mil) thick, but microscopic examination showed that the heat seal layer could be uniformly drawn with the polypropylene. Hot tack (1a) and seal (1b) performance were measured along both machine direction (MD) and transverse direction (TD), see 1 , Although highly oriented, the incorporated seals showed excellent appearance with no observable shrinkage. In these examples, seal failure occurred at moderate levels of force that are fully accepted in the industry, and the mechanism of failure was largely shelling rather than tearing or breaking. The mode of failure at the exemplary moderate force levels illustrates the applicability to peelable seals used for many packaging applications are desired. The hot glue measurement, see also 1 , illustrates values suitable for heat sealing at 110 to 120 ° C, a significant advantage over those temperatures required for heat seal layers comprising polypropylene copolymers. Table 5 Examples of coextruded structures A / B Biaxially oriented on a pilot tenter

Table 6 b. MD orientation

b. TD orientation

Claims (17)

Oriented multilayer film comprising: (a) at least one outer layer comprising from 50 to 100% by weight of ethylene copolymer having a density of from 0.900 to 0.935 g / cm ³ and a composition distribution breadth index (CDBI) of from 50 to 95%, (b) one A polypropylene core layer, wherein the at least one outer layer is in contact with the propylene core layer, and (c) a second outer layer, wherein the second outer layer is in contact with the propylene core layer, wherein the film is coextruded through the at least one outer layer, the core layer and of the second outer layer and subsequent orientation except random copolymer of propylene and 3 to 6% by weight of ethylene or terpolymer of propylene, ethylene and butene as the second outer layer. A film according to claim 1, comprising: (a) two outer layers with 50 to 100 wt .-% of the ethylene copolymer and (b) a polypropylene core layer in contact with the outer layers, in which the film by co-extrusion of the at least two outer layers and the core layer and subsequent orientation. A film according to claim 1 or claim 2, wherein the at least one outer layer comprises a mixture of at least 50% by weight of the ethylene copolymer, being about it In addition, lower levels of substantially compatible ethylene-based Homopolymers or copolymers are present. The film of claim 3, wherein the substantially compatible ethylene-based homopolymers or copolymers are selected from homopolymers or copolymers of ethylene and one or more C ₃ to C ₁₂ alpha-olefins, cyclic olefins, vinylaromatic and polar vinyl monomers. The film of claim 4, wherein the mixture comprising ethylene and one or more C ₃ to C ₁₂ α-olefins has a total density of 0.910 to 0.925 g / cm ³ and a melt index (MI) I _2.16 , determined according to ASTM D 1238 (190 ° C, 2.16 kg), from 0.7 to 5.0 g / 10 minutes. A film according to claim 4 wherein the copolymers of ethylene and one or more of cyclic olefins, vinyl aromatic and polar vinyl monomers contain from 2 to 5 mole percent comonomer and melt index (MI) I _2.16 , determined according to ASTM D 1238 (190 ° C, 2.16 kg), from 0.7 to 5.0 g / 10 minutes. A film according to any one of claims 3 to 5, wherein the substantially compatible ethylene-based homopolymers or copolymers are selected made of LDPE, plastomers, LLDPE, MLDPE, HDPE. A film according to any one of claims 3 to 6, wherein the substantially compatible ethylene-based homopolymer or copolymer VLDPE having a density of 0.915 g / cm ³ or less, including plastomeric ethylene copolymers with C ₄ to C ₈ α-olefins having a density of 0.870 to 0.915 g / cm ³ . A film according to claim 8, wherein the VLDPE has a density of 0.915 g / cm ³ or less including plastomeric ethylene copolymers with C ₄ to C ₈ alpha-olefins having a density of from 0.870 to 0.915 g / cm ³ in an amount to 30 wt .-% is present. A film according to any one of claims 1 to 9, which is biaxially oriented is. A film according to any one of claims 1 to 10, wherein the ethylene copolymer has a molecular weight distribution (MWD) of 1.8 to 3.5 and a melt index (MI) I _2.16 , determined according to ASTM D 1238 (190 ° C, 2, 16 kg), from 0.5 to 10 g / 10 minutes. A film according to any one of claims 1 to 11, wherein the ethylene copolymer has a density of 0.910 to 0.925 g / cm ³ . A film according to any one of claims 1 to 12, wherein the ethylene copolymer has a melt index (MI) I _2.16 , determined according to ASTM D 1238 (190 ° C, 2.16 kg), of 0.7 to 8.0 g / 10 minutes has. A film according to any one of claims 1 to 13, wherein the ethylene copolymer has a broad index the composition distribution (CDBI) of more than 55%. A film according to any one of claims 1 to 14, wherein the propylene core layer Comprising compositions or mixtures with isotactic propylene. A film according to any one of claims 1 to 15, wherein the propylene core layer Propylene polymers having a melt flow rate (MFR) determined according to ASTM D 1238 (230 ° C, 2.16 kg), from 1.0 to 40 g / 10 minutes. A film according to any one of claims 1 to 16, wherein the following Orientation using a tenter orientation method carried out becomes.